Radio receiving system



Patented Oct. 5, 1926.

UNITED STATES,

1,602,086 PATENT OFFICE.

cnnsrnn. w. axon AND nnwann w. KELLOGG, or scminnc'ranx, new Yonir, assmnons 'ro GENERAL ELECTRIC conramr, A conronarron or new Yonx.

RADIO RECEIVING SYSTEM.

7 Application filed July 15,

Our present invention relates to radio receivings stems and more articularly to an improve arrangement D an antenna for receiving purposes. w

This application is a continuation in part of our former application, Serial No. 372,- 938, filed April 10, 1920.

One of the objects of our invent1on 1s to provide a receiving antenna which will be an eflicient means for receiving radio s1 nals from a desired direction to the su stantial exclusion of signals coming from other directions. Another object of our invention is to provide an antenna which, although it may not be tuned. for the irequeue of the signaling waves to be received, will e highly selective to these waves. Still another object of our invention is to provide a receiving antenna which will give which have previously been employed for receiving purposes.

In carrying our invention into eii'ect we make use. of a long horizontal receiving antenna whicli'may be in the 'form of a conductor with ground connections at the ends, extending preferably approximately parallel to or at an acute angle to the directlon of transmission of the signals to be received. This antenna is so constructed that electrical waves of signal frequency travel therethrough at a velocity as nearly, as possible equal to the velocity at which signaling waves in space will travel along the line. Assum ng that the antenna lies parallel to the direction of travel of the signaling waves, this will be the velocity of light. If electrical waves travel through the antenna at the same velocity as that at which the signaling waves travel along its length the signaling currents induced in the antenna will be very small at the end nearest thetransmittin station and increase progressively along t e length of the antenna becoming a maximum at the end farthest from the transmitting station.

In case the natural capacity andinduc- Y tance of the antenna are not of the proper values to give the desired electrical wave velocity for the signal frequency, it is possible to modify the characteristics of the antenna in such away as to produce the desired wave velocity for the frequency in question. In, some cases this desired velocity maybe equal to the velocity of light while in other a more favorable stray ratio than antennae 1821. Serial ll'o'. 485,050.

cases it may (lifter therefrom as will be more fully-set forth in our s cification.

The novel features w ich we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, both as to its organization and method of operation, together with ways in which the articular ob ects thereof may be attained will best be 1 understood by reference to thefollowing description taken in connection with the accompanying" drawing inwhich Fig. 1 illustrates diagrammatically one way in which our invention may carried into effect. Figs. 2, 3 and 4 illustrate modified ways in which the wave velocity on a large antenna may be adjusted, and Fig. 5 shows typical curves illustrating the variations in signal strength along the length of the antenna.

Consider first a simple horizontal receiving antennae 1, as indicated in Fig. 1, which extends from the receiving station at end 3 of the antenna towards the transmitting station 6 fromwhich the desired signals are coming. The operation of such an antenna in receiving signals may be explained as follows: Assume that the signaling waves in space are traveling from station 6 in the direct-ion of the antenna, then at the end 2 of the antenna asmall'current will be induced which will be propagated as a wave along the antenna toward the end 3. If the velocity of this small current wave in the antenna is equal to the velocity of the signaling wave in space, this current wave will grow as it approaches the end 3 by continuously absorbing small additional amounts of energy from the ether waves vsince the two waves are traveling along in phase with each other. From this analysis it appears that, if the constants of the antenna are such that the current wave travels at the same velocity as the ether wave, the longer the antenna the greater the current which will be received. There will of course be a maximum length beyond which nothing Even assuming because the waves on the antennaxwillfinally v reac I an amplitude equal to the amplitude of the ether waves, that is, rerad1at1on w1ll balance the received energy. This condition may be referred to as saturation. If however, the velocity of the current wave in the antenna is not quite the same as at of the ether wave then for a certain distance the two waves will add, but a point will finally be reached where one wave willbe so far in advanceof the other that the two will.

be in phase opposition. Interference will then occur and the current wave will decrease to zero and then a new wave will be started .and built up. Under these conditions the along the antenna between maximum and minimum will depend upon the difference in the velocity of the electric wave and the antenna and the ether wave surrounding it in space. If the velocities differ very little a long receivin antenna can be .used to advantage, but i the velocities are con sider-.

ably different there may be no advantage in using a greater length of antenna than that which will give the first maximum for thedesired signal frequency.

Fig. 5 illustrates the variation in current" strength in the antenna under the two different conditions of operation which we have described. In this figure the ordinates represent signal strength and the abscissae represent distance along the antenna. Curve B shows the increase in current strength along the length of the antenna when the current ,wave in the antenna and the ether Wave travel at the same velocity. This shows that the current increases along the length of the antenna quite rapidly at first, then more slowly due to saturation'and line losses. It is assumed that the distance represented by this curvejis the maximum length of antenna which can be used toadvantage and this maximum length may be'equal to several -.wave lengths. Gurve C shows the variation in current strength along the length of the antenna for one case when the current wave and the ether wave travel at different velocities. Here the current increases until a maximum is reached at the point D; then decreases to a minimum at point E; increases to a second maximum at point F; and decreases again to a minimum at point G. Since these two maximum points are approximately of the same value it is apparent that for the velocity relations assumed in the curve C nothing will be gained in signal ployed rub strength by using a greater len h of antenna than that represented by t e distance AD althou h there ma be a gain in stray ratio due to the sharper c irectivity of an antenna which exceeds this length. Curve H represents the variation in current strength along the len thof the antenna for another case in whic the current wave and the ether wave travel at different velocities. Here the maximum current is reached at the point I and the minimum point is reached at the end of the antenna. Many of the lon antennae hitherto used, em-

tier covered wire, buried, submerged in water, or on the surface of the ground. These types of construction give low velocity and high attenuation, both of which efl'ects limit the length of antenna which can be advantageously employed, optimum length of about one-eighth of a wave length (of the ether waves) having been observed in tests. The conditions necessary in order to secure the benefits of longer an- :ennae are high velocity and low attenuaion.

For-signaling'waves traveling in the 0pposite direction, the currents will build up in the same manner. If these are reflected at the end 2, Fig. 1, they will return to 3 and afl'ect the receiving apparatus, giving the antenna bi-directional properties. Reflection may be avoided by grounding the end 2 through a non-inductive resistance 5 of a value equal to or or approximating the surge impedance of the antenna; which is 6 where L and O are the inductance and capacity of the antenna per unit length. adopting this or any other expedient w ich eliminates reflection from the far end the antenna will be given marked unidirectional properties and will be highly selective for signals coming from one direction to the exclusion, not only of signals coming from other directions but to static impulses coming from other directions as well. The greater the length of the antenna compared with the signal wave length, the more sharply directional the antenna will become.

The dam ing resistance 5 in Fig. 1 might be replace by a receiving set having an equivalent impedance without impairing the usefulness or undirectional property of the antenna when used with the receiving circuit 4. If the receiving circuit 4 also has an impedance approximately equal to the surge impedance of the antenna, then a receiving circuit located at the end 2 will receive only slgnals coming in the direction 3-2, or opposite to those received by the receiving circuit'4. A long antenna may thus serve two receiving stations, for signals coming from opposite directions and there will be no loss of elficiency by thus makin the antenna serve a double purpose. In Iact, for maximum efficiency the receiving circuits should be designed to have an effective impedance equal to the antenna surge impedance.

In accordance with theoretical considerations, if an antenna were to be freel suspended and if the surface of the cart constituted a perfectly conducting parallel plane, current waves would travel through the antenna conductor at a velocity equal to the velocity of light. In ractice, this theoretical condition may be dlfilC-lllt to obtain because of ground resistance and be cause of the necessity for providing supports for the antenna. v The effect of these supports may be to ad shunt capacity to the line without causing any compensating change in the other line constants. The effect of the excess shunt capacity may be neutralized for continuous waves of a particular frequency, by means of shunt inductances connected at frequent intervals between the antenna and ground. Or the effect of excess shunt capacity in slowing down the rate of wave propagation may be compensated for by the insertion of condensers in series with theline conductors, thereby neutralizing. part of the series inductance and increasing the wave velocity. Such shunt inductances or series condensers should be sufficiently close together (in no case more than wave length apart) to give substantially the effect of distributed shunt inductance or series capacit it for the frequency which is to be receive By choosing proper values for the inductances and condensers the wavevelocity on the line for continuous waves of any specified frequency may be made equal to or greater than the velocity of light. If the line has been adjusted to give a velocity of wave propagation equal to the velocity of light for a specific frequency, then for continuous sinusoidal waves the apparent velocity of propagation will be greater than the velocity of light for lower frequencies than that for which the line is adjusted, and will be less than the velocity of light for signals of a higher frequency than that for which it is adjusted.

An alternative method of correcting wave velocity on a long antenna consists in'the introduction at suitable intervals of links of artificial line, which will act in sucha way as to retard or advance the phase of the wave. Thus the introduction of a link consisting of series condensers and shunt inductances will have the effect of advancing the phase or increasing the average wave velocity for the antenna as a whole, while the introduction of links consisting of seriesinductances 9 and shunt condensers 10, as

' shown in Fig. 3, will produce a delay or slow down the average wave velocity of the antenna. For continuous wavesthe introduction of a delay link slightly less than one wave length long will by retarding the phase of the wave by something less than one cycle, have an effect equivalent to advancing the base or increasing the wave velocity, while or single impulses or highly damped waves the effect would be to break up the resulting disturbance on the antenna into several relatively feeble impulses.

Artificial lines or (links of the kind just described may be introduced without causing seriousrefiection losses in the antenna, either by making the linksalike and spaced sufliciently close together, provided the links themselves are short, or by designing the artificial lines so that their surge impedance is equal to thesurge impedance of the unadjusted antenna.

The above described methods of adjust irfg velocity give different velocities for different frequencies. This "permits of selectivity based on frequency, in addition to the selectivity offered by reason of the directive properties of the antenna. For example, referring to the'curves of Fig. 5 an interfering sending station might be located in a direct line with the transmitting station whosesignals it is desired to receive. As suming that the wave length of the signal transmitted from this interfering station differs from that of the desired signals for which the antenna is adjusted, the velocity of its waves on the antenna can be made to dlfier from their velocity in space by such an amount that a node, such as shown at points E or G, of curve C, Fig. 5, will occur at the point where the receiving apparatus is located.

If such is the case the interfering station will produce substantially no effect upon the receiving apparatus. Under other conditions, supposing two currents in the antenna from two stations in line with each other to be represented by the curves 0 and H, Fig. 5, reception could be accomplished from the station represented by the curve H by locatin the receiving apparatus at the p oj nt I w ere this current is large and the current of curve C is substantially a minimum. 4 I

If the natural capacity and inductance of the antenna have substantially the values required to give a velocity of wave propaga- .tion in the antenna equal to the velocity of light such an antenna would have the same wave velocity for all frequencies and while possessing the desired directive properties would not be selective for frequency. Under these circumstances it may be desirable to insert series inductances'7, Fig. 1,which of themselves would lower the wave velocity on the antenna, and to neutralize the effect of .these'inductances for a particular frequency, by inserting series condensers 8.

It may also be desirable in some cases in (ill 'tenna will alternatel order to further sharpen the frequency sclectivity of the line, to use added shunt capacity 11, as a means of slowing down the wave velocity and to neutralize-this by shunt.

inductances 12 as indicated in Fig. 2.

These added conductors connecting the antificial line consisting of series con ensers and shunt inductances, and for all frequencies above signaling frequency the line becomes analogous in its action to a low pass filter, or lumped artificial line consisting of series inductances and shunt condensers.

The filter action of the adjusted antenna ofiers a means of eliminating undesired sig nals or disturbances having a wave length differing from that of the desired signal.

= This feature is under control by properly.

proportioning and spacing the inductances and condensers, in accordance with well established principles. An equivalent action may be obtained by using a filter in the receiving station. I

Another interesting property of this type of antenna is its efiect in stray elimination. Consider an antenna of this type which was normally slow, for example, a rubber covcred wire or iron wire, but which is speeded up by series condensers for a particular freuency. For static impulses of steep wave f ront the series condensers will act practically as zero impedance and the static will be propagated along the line at its normal low velocity. Sim1larly, if shunt inductances were. used for speeding up, these would act as infinite impedance for static impulses and the static wave would be propagated at the low normal velocity of the line.

This means that the static current in the anbuild up and then build down by inter erence with the static wave in the ether and if there happens to be a certain particularly eli'ective frequency in the static which is troublesome in exciting the receiver tuning circuit it is possible to locate the receiving apparatus at an interference node for static. The signal being a continuous wave will progressively build up to a large value at the point selected for the receivlng apparatus.

It is not necessary for good results that an antenna of the ty e we have been describing be placed para lel to the direction of travel of the waves to be received althou h approximate parallelism may normally be desirable. If the direction of travel of the waves in space makes an angle 0 with the Wave front with the antenna (i. e. the point of maximum instantaneous induced potent1al on the antenna) Wlll move along the antenna with a velocity a cos 0 in which 0 is the velocity of light, and in order for such a wave to produce the maximum effect in the receiving apparatus, the

velocity of propagation on the antenna should be J2. cos 0 Thus by producing an efi'ective wave velocity onthe antenna somewhat greater than the velocity of light, the antenna can be made to show its maximum sensitivenessfor waves coming from an angle.

Since the form of the current distribution curve C or H, Fig. 5, depends upon the difference between the velocity of waves on the antenna and the velocity with which an ether disturbance travels along the antenna, which is C there are certain values of the angle 0 which The adjustment of wave velocity on an an-' tenna can be made in such a way as to give not only a desired velocity for one'fre uency, but at the same time to give a desire velocity for a second frequency. For example,

.suppose that the antenna points directly toward one transmitting. station whose signals are to be received and that a second transmitting station of greater wave length lies at an angle 0 with the direction f the receiving antenna. For signals from the first station thewave velocity on the antenna should be that of light, while to obtain maximum intensity for signals from the second station the velocity should be cos 0 where 0 stands for the velocity of light. If an antenna is employed whose natural constants are such as to ive a wave velocity C, no adjustment woulg be necessary for the antenna, then the point of intersection of a first station but the wave velocity would be v velocity at which the desired signaling waves too low for strongest reception of signals from the second station. If now series inductances are introduced, and their react ance neutralized by series condensers for the frequency of the signals from the first station, the wave velocity for these signals will be unchanged, but the velocity will be increased for the longer waves of the second station. The larger the values of inductance and capacity the greater will be the velocity for the longer waves. Hence values of in-. ductance and capacity can be chosen which will give the desired velocity wave velocity on the antenna for waves of a different frequency than those desired may then be such that a point along the length of the antenna may be selected which will be a node for interfering Waves.

An antenna having a velocity less than that of light may show sharper directivity than an antenna of the same len h having full velocity, because while there is a loss of signal intensity as a result of the low velocity on the antenna, the effects of disturbances coming from other directions may be reduced in still greater proportion. If the construction of the antenna line is such as to give a velocity nearly equal to that of light, improved directive properties will under some circumstances result from slowing down the line by loading it either with capacity to ground or with series inductance.

What we claim as new and desire to se-- cure by Letters Patent' of the United States,-

1. A receiving system for radio signals comprising a antenna extending in a direction at an angle to the general direction of transmission of the waves to be received and having a length at least substantially as great as the wave length of the signals to be received, said antenna being so constructed and its constants so adwsted that electric waves. induced therein will be propagated along its length at a velocity substantia ly equal to the travel along its length in the ether.

2. A receiving system for radio signalssubstantially horizontal comprising a substantially horizontal antenna extending in a direction at an angle to the general direction of transmission of one set of waves to be received and having a length at least substantially as reat as the wave length of the signals to e received, said antenna being so constructed and its constants so adjusted that electric waves induced therein by signaling waves coming from more than one direction will be propagated along its length at velocities substantially equal to the velocities at which the corresponding desired signaling waves travel along its length in the ether.

3. A receiving system for radio signals comprising a horizontal antenna having a length at least substantially as great as the wave length of the signals to be received and having such natural constants that current waves will be propagated therein at a velocity substantially equal to the velocity of light and means for. reducing the velocity of propagation of current waves therein in order to obtain improved directive properties.

4. A receiving system for radio signals comprising a horizontal antenna having inserted thereinat intervals along its length parallel sets of series inductances and capacities, each set of series inductances and capacities being so proportioned that current waves of one particular frequency will be propagated along the length of the antenna at a velocity substantially equal to the velocity of light.

5. A receiving system for radio signals comprising a horizontal antenna having inserted therein at intervals along its length parallel sets of series inductances and capacities, each set of series inductances and capacities, being so proportioned that current waves of one particular frequency will be propagated along the length of the antenna at a velocity substantially equal to the velocity at which the corresponding signaling wave travels along its length in the ether.

6. A receiving system for radio signals comprising a substantially horizontal antenna having a length at least substantlally as great as the wave length of the signals to be received and said antenna being so consti 'ucted and ad'usted that electric waves induced therein by signaling waves coming from diiferent directions at least one of which is different from the direction in which the antenna extends will be propagated alon its length at velocities substantially ua. to the velocities at which the correspon in signaling waves travel along its length in t e ether. I

In witness whereof, we have hereunto set our hands this 14th day of July, 1921.

CHESTER w. Rios. EDWARD W. KELLOGG. 

